The fiberglass mats on the market today generally consist of a base of chopped glass fibers ranging in length from 1/4" to 11/2" and diameters ranging between 9 and 16 microns. The chopped glass fibers are usually bonded together by a suitable bonding agent, such as urea resins, phenolic resins, bone glue, polyvinyl alcohols, etc. Preferably, the bonding agent is water resistant. The glass fibers and the bonding agent are usually formed into a mat having a production width of approximately 36" to 48". The mat is passed through an oven in order to cure the bonding agent. There are two generally accepted methods today for making fiberglass mat: the dry method and the wet method.
In the dry method, elongated yarn strands, which are usually continuous, are often placed in the center area of the mat or sheet to provide tear resistance. Such an arrangement, however, has the disadvantage of causing layering, i.e., a separation of the mat into a plurality of laminae or sheets. This is caused by the central layer of yarns weakening the mat in mechanical strength and destroying its homogeneity, thus causing or allowing easy separation of the mat into two or more parts.
An example of a mat formed by means of the dry process, and a machine for forming that mat, has been shown in U.S. Pat. No. 2,731,066 to Hogendobler, et al. Those patentees recognized that a mat consisting only of chopped fibers and a bonding agent resulted in a product with very little tear strength in any direction. Consequently, they proposed to install continuous strands of fiberglass in the product. They therefore proposed to develop a mat having reinforcing strands arranged in a haphazard pattern and, in addition, a plurality of parallel reinforcing strands. However, in that patent it is disclosed that the reinforcing strands of both types are randomly mixed, considered in vertical cross-section, into the resulting product, without providing for any separation between the different types of strands. In fact, in many instances either or both types of the reinforcing strands are positioned along, or extend to, one of the surfaces of the mat. Consequently, while those strands do provide additional strength, relative to a mat having only the chopped fiber bonded together, the resultant product is still insufficiently strong to withstand tearing under common usage.
In this country, for example, roofing materials are applied to new buildings at an extremely rapid rate. As a result, they must be able to withstand rather rough handling. In many instances, matting formed by the dry process and transformed into roofing materials, even using the Hogendobler reinforcing strands, is insufficiently strong to withstand the rough handling. This results from several reasons. One of the reasons is that dry chopped fiber does not disburse uniformly across the surface of the mat being produced, and thus the resultant product does not have uniform strength. Additionally, the reinforcing strands which are indiscriminately mixed throughout the thickness of the mat cause the resultant product to lact a proper homogeneity, with a resultant loss in tear resistance strength.
Consequently, it has been found that although the products formed in accordance with the Hogendobler disclosure are greatly improved over those which do not utilize reinforcing strands, they are still insufficiently strong to withstand rough handling and usage without making the mat so thick that the weight increase negates the original reason for using the reinforcing strands. In other words, since the random yarn and straight yarns are not separated, the tear resistance strength, at least in some directions of tearing force application, is significantly reduced.
The wet process has been developed over the past few years in order to be able to produce fiberglass mat at a far more rapid rate than is available using the dry process. Initially, the process was developed to produce a product having only chopped fibers and bonding agent. Consequently, there was no significant tear strength in any direction for any suitable product. In many areas of the world, such as Europe, such mat is quite satisfactory for being transformed into roofing. Since construction proceeds at a more leisurely pace in those areas, the handling of roofing materials is far more gentle and not so much strength is needed in the product. In this country, however, roofing must be produced at about three times the rate as it is produced in Europe and the resulting products must be strong enough to withstand the rough handling required by speed in application.
Consequently, it has become very desirable to be able to produce a fiberglass mat by the wet process having strength which at least meets and preferably exceeds that available through the dry process, such as taught by Hogendobler, et al.
As a further problem discovered in the prior art products, it has been found that there are some instances in which it is highly undesirable to use reinforcing strands which are installed in a straight line along the length of the mat being produced. During the production of matting, the strands are drawn from the spools by some mechanism and applied to the location of initial mat formation. As these strands are drawn from the spools, there is a possibility that, occasionally, the strand will "hand-up" temporarily until it can be pulled free by continued application of a pulling force. Such a hang-up might be caused, for example, by a slight snag in the line which causes it to bind against an adjacent winding of the strand on the spool. When this occurs, tension can be imposed on the entire line up to the point at which curing has finally occurred in the oven. This is closely analogous to what happens to a fishing line when a fisherman raises the tip of his rod to impose tension on the line. In the production of fiberglass mat, this imposition of tension on the longitudinal strand, even momentarily, usually causes a disruption and disorientation of the chopped fibers. Such disruption may occur in the fibers both above and below the strand. The result is a line of weakening extending along the entire mat from the point of finished curing to the initial mat formation location. It is very difficult to discern this line of weakening caused by such "fishlining".
If the mat having the weakened section is transformed into roofing, for example, the disorientation of the chopped fibers usually results in a "ripcord" or straight line crack developing along the length of the product. That line of weakness which develops into a crack can then cause a crack to develop in all of the layers of roofing material formed on a roof, whether above or below the mat section containing the crack. In fact, such continuous cracking has sometimes occurred in such a manner that it appeared that a vandal had pushed a circular handsaw along the length of the roof.
Obviously, this is an extremely dangerous possibility since the premature destruction of roofing materials can result in severe damage to a building. In most cases, it is impossible to prevent the cracking since the "fishlining" cannot be seen since there is no visible disorientation of the straight line strand, considered in a horizontal cross-sectional plane, at least.
In some instances, it may also be desirable to provide a mat having other than absolutely straight reinforcing strands. Such a need might arise from a finished product requirement relating to bending. For example, if bending occurs along a straight strand, that strand presents a very narrow reinforcing bend area and it will serve as a "ripcord" and allow the product to crack and/or break. On the other hand, a semi-straight or sine wave-type of strand configuration will present a much wider reinforcement. Consequently, any bending which may occur is far less likely to result in damage to the product.
In many cases, after their production such mats are transferred to a machine upon which they are cut apart and provided with slots so as to form a roofing shingle of a well-known configuration. Such shingles are usually provided with slots which extend from one edge of the shingle to a predetermined distance into the body of the shingle. This allows a single shingle to give the appearance of three of more smaller shingles, separated by the slots, on a finished roof.
When such shingles are installed upon a roof, a bonding adhesive is used to hold the exposed edges in place. Until that adhesive becomes completely cured, the exposed portions of the shingle, i.e., those portions between the slots, are susceptible to repeated bending by wind. Depending upon the particular configuration of the reinforcing strands within the mat, such repeated flexing or bending of the exposed portions of the shingle can cause those exposed edges to crack or break off. Such cracking or breaking often occurs along the line extending between the inner ends of adjacent slots.
If such cracking or breaking occurs, additional time and expense are incurred in providing the labor and additional shingle materials for replacing the broken shingle. In some instances, the removal and replacement of a single shingle may require that a number of shingles be replaced due to any damage which might occur to the others when the broken shingle is removed.
In order to reduce or substantially eliminate the possibility of the breaking of such shingles, it has become necessary and desirable to produce a fiberglass mat having a significant strength to resist tearing. Such a mat should not be susceptible to "fishline" or "ripcord" damage, and it should be producible at a very high speed. The mat should also be provided with some form of structural strengthening which will prevent cracking or breaking of the shingles when the exposed edges, between the slots, are acted upon by wind at a time when the bonding agent holding the shingle to the roof has not cured completely.